Fig. 7. Relationship between maximum speed in each prolonged glide measured at the depth of >100 m, and pitch at the moment when the speed was recorded, for weighted (solid diamonds) and unweighted (open diamonds) conditions. Pitch represents the angle between the long axis of the seal's body and the water surface, with negative values indicating descent. Theoretical terminal speeds for several body densities are shown as colored lines, with the density values in kg m^-3 indicated by the numbers beside the lines. Strictly speaking, the theoretical lines are different between the conditions because of the different mass of the object (seal + weight=46.65 kg for the weighted condition; seal=45.2 kg for the unweighted condition; see Eqn 4) and should be shown separately. However, the difference in mass corresponds to a difference in theoretical terminal speed of only 1.6%. For clarity, we show the theoretical lines common to both conditions, based on the mean mass (45.9 kg).